Swelling agents for cellulose acetate



May 29, 1956 W. F. STAHL ET AL SWELLING AGENTS FOR CELLULOSE ACETATE Filed March 4, 1952 ATTORNEYS.

United States Patent() SWELLING AGENTS non cELLULosE ACETATE William F. Stahl, Kenilworth, and Fred V. Collins, Des Plaines, Ill.; said Collins assigner to said Stahl Original application May 3, 1950, Serial No. 159,756. Divided and this application March 4, 1952, Serial No. 274,761

5 Claims. (Cl. 106-316) This invention relates to a chemical bath particularly useful in making bobbins or coil forms of the type commonly employed in industry for holding transformer windings and the like. This application is a division of our earlier copending application, Serial No. 159,756, tiled May 3, 1950, now Patent No. 2,644,651.

In that parent application and in our other copending divisional application, Serial No. 274,762, tiled March 4, 1952, we have described and claimed a novel bobbin and a novel process for making the same. The process of our invention involves subjecting a plastic-covered core to treatment in a novel chemical bath; the composition of the bath is the particular subject matter to which the present divisional application is directed.

Coil forms or bobbins of the type here under consideration have a very extensive use in the electrical industry, millions of them being used annually in the United States as supports for electrical windings. Such a form of bobbin consists, in general, of a corewhich may be circular, square, or rectangular in cross sectionprovided at its respective ends with terminal flanges which extend radially outward at right angles to the axis of the core. In the most commonly used form, the core is made of laminated paper and the terminal tlanges are formed of hard ber.

In the prior art, so far as we are aware, such coil forms have been universally made by placing the flanges on the ends of the core and then swaging the core ends to lock the flanges in place. In many cases, to prevent the swaging action from forcing the flanges too far inward along the core, the core has been provided with a central zone of larger dimensions than its terminal zones, as by covering the laminated paper core with an additional sleeve of paper or ber. This central Zone of increased dimension would, during the swaging operation, serve as an anchor for the anges and, after swaging, the flanges would be securely locked between the outer ends of the increased-dimension Zone and the swaged extremities of the core proper.

The mode of manufacture just described has been in universal use for a number of years and has been highly satisfactory so far as the performancey of the end product is concerned. It is a relatively expensive manufacturing technique, however, for the reason that each individual form or bobbin must be subjected to mechanical swaging-an operation which calls for expensive machinery and which consumes considerable time.

Our novel process disclosed in said parent application, Serial No. 159,756, tiled May 3, 1950, has provided a means of making bobbins or coil forms fully as satisfactory as bobbins made by the swaging technique and at a much reduced manufacturing cost. Bobbins made by our process have very great mechanical strength, are consistently uniform in dimensions, and can be processed in batches of several hundred or thousands at one time, in contrast to the swaging of the prior art which must be performed individually on each bobbin.

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The major object of the aspect of our invention specilically treated in this divisional application is to provide a novel chemical bath in which bobbins or coil forms made according to our method can be treated en masse to anchor the terminal flanges to the core by chemical action, without necessity for swaging.

Another object of our present invention is to provide a chemical bath, suitable for use in our novel process for making bobbins, comprising a plurality of solvents having different Working speeds, in combination with a suitable swelling agent. l

Other objects and advantages of our invention will appear as the specication proceeds.

The appended drawing shows an illustrative embodiment of our novel coil form, made according to the process of our invention. In the drawing, Figure l is a perspective view of a coil form or bobbin embodying our invention; Fig. 2, a side view in cross section of the coil form of Fig. 1 as it appears prior to assembly, with the core and terminal flanges shown separately; Fig. 3, a sectional view similar to Fig. 2 but showing the appearance of our coil form after the terminal flangeshave been placed in correct position on the core and anchored therein by being subjected to treatment in a chemical bath; and Fig. 4, a greatly enlarged fragmentary View of a portion of Fig. 3, showing in detail the manner in which the terminal ange is secured to the core, after chemical processing.

In carrying out the process of our invention, we pro-A vide laminated paper cores, which may be conventional, with a thin layer of plastic, preferably cellulose acetate,

vWound over the surface of the core to form a continuous single layer thereon. Such winding can easily be done in the course of manufacturing the cores. On the drawing, the core of the coil form therein illustrated is denoted 11 and the plastic layer deposited thereon is denoted 12.

The terminal flanges, which may be conventional in all respects, are denoted respectively 13 and 14. In the illustrated embodiment, each of the flanges is equipped with an axial indentation 15, and the indentation 15 surrounds a central aperture 16 which conforms in shape and size to the surface of core 11 as covered by plastic layer 12. That is, terminal flanges 13 and 14 are stamped with central apertures which will tit snugly but readily over core 11.

In the case of the particular embodiment shown, providing flanges 13 and 14 with the indentations 15 permits the construction of a coil form in which the outer perpendicular surfaces of flanges 13 and 14 are flush with the respective ends of core 11, there being nevertheless a small zone 17 of core 11 projecting beyond the apertures 16, as may be best seen in Figs. 3 and 4.

Flanges 13 and 14 are placed over core 11 in the position which it is desired they occupy when the coil form is finished. This may be done mechanically or by hand, according to the magnitude of the manufacturing operation. The coil form, along with as many hundreds or thousands of similar coil forms as the size of the facilities will permit, is then placed in a chemical bath operative to soften and swell the plastic layer 12. Exposure to the bath for an interval from one to ve seconds results in substantial swelling of all the plastic layer 12 which is able to contact the bath. As a result, the plastic layer promptly swells, as indicated in Figs. 3 and 4, and securely locks the flanges 13 and 14 into proper position on core 11.

After the forms have been removed from the bath, they are dried-preferably by exposure to controlled heat in an oven-and are then ready for shipment or use.

We have found that the mechanical strength of coil forms made according to our invention is fully equal to,

3 and in some `ca'se's exceeds, the mechanical strength of similar coil forms made according to the prior-art swaging method.

The chemical composition of the treating bath may take any desired form within wide limits. ln general, the treating bath should comprise a moderate 4amount of a swelling agent combined with substantially greater quantities of solvent. While wide discretion in the choice of solvents and their proportions may be allowed, the composition employed will greatly influence the length of time required for the bath to effect the swelling and setting actions which in our invention accomplish the anchoring of the flanges to the core. We have found that effective yet extremely rapid results can be obtained when the swelling agent is combined with a plurality of solvents having radically different time characteristics. In our most satisfactory compositions, we have employed a relatively small quantity of a mild solvent combined with larger and substantially equal quantities of an active solvent and an extremely active solvent.

The swelling agent, when cellulose acetate is employed as the plastic coating on the core, may be selected from among the ketones; we have found methyl isobutyl ketone particularly satisfactory.

While it is not necessary in most cases, we have found helpful the addition to the bath of a small quantity of plasticizer. This ingredient prevents the plastic layer from becoming brittle and thus increases the ability of the completed bobbins to withstand mechanical abuse. We have found dibutyl phthalate and tri(2 chloroethyl) phosphate satisfactory plasticizers for this purpose.

Following are two examples of bath compositions found to be highly successful in practicing the method of our invention:

Example I A bath was made up of 60 parts of tetrahydrofuran, an extremely active solvent for cellulose acetate, 50 parts of acetone, a somewhat less active solvent, and 20 parts of ethylene glycol monomethyl ether, a mild softening solvent, and parts of methyl isobutyl ketone, the swelling agent. The ingredients were mixed thoroughly at room temperature, and the bath was then ready for use. It was found that excellent results were obtained with this bath when the coil forms were placed in it for a period of ve seconds.

Example Il A chemical bath for carrying out our invention was prepared by employing 64 parts of furfural, 40 parts of ethylene glycol monomethyl ether, and 40 parts of methyl isobutyl ketone. These ingredients were mixed thorough*- ly `at room temperature and to them was added one part of dibutyl phthalate. The resulting bath was employed at room temperature in the practice of our invention. It was found that immersion of the coil forms in the bath for intervals of one to tive seconds effectively swelled the plastic coatings on the cores and provided excellent anchorage for the terminal flanges.

While we have in this specification described in detail certain specific examples of chemical baths falling within the scope of our invention, it is to be understood that those are illustrative only. Many variations in composition, within the scope of the appended claims, will occur to persons skilled in the art and may be employed without departing from the spirit of our invention,

We claim:

l. A chemical bath for rapidly swelling thin layers of a plastic from the class consisting of cellulose acetates, consisting essentially of a mixture of organic solvents for the plastic, one of the solvents being an active solvent and taken from the group consisting of tetrahydrofuran and furfural and being in the proportion of about 60 parts, and a less action solvent taken from the group consisting of acetone and ethylene glycol monomethyl ether and being in the proportion of from about 40 to parts, and about 10 parts of methyl isobutyl ketone.

2. A chemical bath for rapidly swelling thin layers of cellulose acetate, consisting essentially of a mixture of organic solvents having dilferent working speeds, one of said solvents being tetrahydrofuran in about parts, acetone in about 50 parts, and ethylene glycol monomethyl ether in about 20 parts, and about 10 parts of methyl isobutyl ketone swelling agent.

3. A chemical bath for rapidly swelling relatively thin layers of cellulose acetate, consisting essentially of a mixture of organic solvents having dierent working speeds, one of said solvents being furfural in about 64 parts, another being ethylene glycol monomethyl ether in about 40 parts, and m-ethyl isobutyl ketone in about 40 parts. I

4. A chemical bath for rapidly swelling relatively thin layers of cellulose acetate, consisting essentially of a mixture of organic solvents having different working speeds, one of said solvents being tetrahydrofuran in about 60 parts, acetone in about 40 to 50 parts and about l0 parts of methyl isobutyl ketone swelling agent.

5. A chemical bath for rapidly swelling relatively thin layers of cellulose acetate, consisting essentially of a mixture of organic solvents having different working speeds, one of said solvents being tetrahydrofuran in about 60 parts, ethylene glycol monomethyl ether in about 40 to 50 parts, and about 10 parts of methyl isobutyl ketone swelling agent.

References Cited in the le of this patent UNITED STATES PATENTS 2,002,800 Schrouth May 28, 1935 2,009,347 Reid Nov. 16, 1937 2,100,425 Bent et al. Nov. 30, 1937 2,150,334 McKittrick et al Mar. 14, 1939 2,242,533 Meigan May 20, 1941 2,288,588 Rieche et al. June 30, 1942 2,319,660 Clark May 18, 1943 2,345,427 Reppe et al. Mar. 28, 1944 2,471,501 Steigleman May 31, 1949 2,563,417 Pessel Aug. 7, 1951 2,666,979 Van Dusen Jan. 26, 1954 

1. A CHEMICAL BATH FOR RAPIDLY SWELLING THIN LAYERS OF A PLASTIC FROM THE CLASS CONSISTING OF CELLULOSE ACETATES, CONSISTING ESSENTIALLY OF A MIXTURE OF ORGANIC SOLVENTS FOR THE PLASTIC, ONE OF THE SOLVENTS BEING AN ACTIVE SOLVENT AND TAKEN FROM THE GROUP CONSISTING OF TETRAHYDROFURAN AND FURFURAL AND BEING IN THE PROPORTION OF ABOUT 60 PARTS, AND A LESS ACTION SOLVENT TAKEN FROM THE GROUP CONSISTING OF ACETONE AND ETHYLENE GLYCOL MONOMETHYL ETHER AND BEING IN THE PROPORTION OF FROM ABOUT 40 TO 50 PARTS, AND ABOUT 10 PARTS OF METHYL ISOBUTYL KETONE. 